Process for the production of light voluminous silicates



United States Patent PROCESS FOR THE PRODUCTION OF LIGHT VOLUMINOUSSILICATES No Drawing. Filed July 5, 1957, Ser. No. 669,971

1 Claims. (Cl. 23110) The present invention relates to a process for theproduction of light voluminous silicates from natural materials whichare especially suited as filters and, for

example, present an active reenforcing filler for rubber. It is knownthat natural silica products, such as kieselguhr, can be used for manypurposes in technology,

for instance, as insulating material or as carriers for catalysts. Suchnatural silicates, are, however, usually 1 not usable as fillers whenfineness of particle size is required and special active properties arerequired. For

such purposes finely divided silica is usually prepared by reaction ofsoluble silicates with acids or salt solutions whereby when specialmeasures, usually complicated, are employed during the reaction orworking up of the silica produced a product of large surface area withmore or less activity is obtained. This activity renders such preparedsilicas suitable as fillers for rubber or rubber-like substances or alsoas carriers for catalysts when the carrier itself is also to exhibitcatalytic properties.

It has also been proposed to convert natural products either completelyor essentially composed of silica, such as sand, kieselguhr, orclay-like substances, into silicates by treatment with alkaline earthmetal hydroxides in the presence of water at elevated temperatures andpressures. A rather strong loosening of the starting material isachieved in this manner and the silicates produced have a greateractivity as a filler than the starting materials. However, when they areused as fillers in rubber some of their properties leave much to bedesiredso that they cannot be used with success in every instance.

According to the invention it was found unexpectedly that finely dividedsilicate products, which are especially well suited as active fillersfor rubber and rubber-like materials and also suited as fillers forother materials or as carriers for catalysts, can easily be obtainedfrom alkali metal-aluminum double silicates by treatment thereof in anaqueous dispersion in the presence of an alkaline earth metal hydroxide,preferably calcium hydroxide, at elevated temperatures and pressures.

The following alkali metal-aluminum double silicates are illustrative ofthe starting materials usable according "to the invention: sodiumorpotassium feldspa'rs, mica minerals, leucite, and lithiumorcesium-containing minerals,..such as lepidolite, petalite, pollucite and"spodumene.

The starting materials can be subjected toithe hydrothermal pressuretreatment either directlyorin pre- In order to ensure the fiowability ofthe material treated it is preferable to work with suspensionscontaining at least 8 parts of water per part of solids.

The quantity of alkaline earth metal hydroxide employed is ofsignificance. The quantity employed is calculated with reference to theSi0 content of the starting double silicate. The quantity of alkalineearth metal hydroxide employed should not be less than 0.5 mol andpreferably be at least 0.75 mol per mol of SiO Especially good resultsare achieved as will appear from the examples given below, particularlywith a view to the suitability of the product as an active filler forrubber when a quantity of alkaline earth metal hydroxide, pref erablycalcium oxide, is employed which is in excess of the stoichiometricquantity calculated upon the SiO, content of the starting doublesilicate. Consequently, according to a preferred embodiment of theinvention the hydrothermal treatment of the starting double silicate iscarried out in'aqueous dispersion with 1.1 to 1.3 mol, preferably 1.15to 1.25 mols, of alkaline earth metal hydroxide per mol of Si0 in thestarting silicate.

The hydrothermal treatment of the aqueous dispersions is carried outunder pressure at temperatures between 150 and 280 C., preferablybetween 180 and 210 C.,

. whereby a pressure of about 18 to 19 atmospheres gauge pressure isattained. The products obtained with the process according to theinvention are voluminous, light silicates whose poured and shakenweights are about V3 to Vs of those of thestarting materials. Thehydrothermal treatment can be efiectively carried out in autoclaves withstrong stirring or in heatable pressure resistant tubes. By connectingseveral autoclaves or tubes in series, the process can be carried outcontinuously, the number of autoclaves and tubes being determined fromthe time required for the treatment and the rate of flow of the materialbeing treated. In batch processes, treating periods of 2 to 4 hours aregenerally sufiicient to effect the conversion of the starting materials.The voluminous products obtained according to the invention have a purewhite color and can be used for many purposes. They have provedespecially suited as fillers for natural or synthetic rubber or otherelastomers in which a reenforcing action is desired. Naturally they canalso be used in other technical applications where inert fillers areused, for example, for weighting paperfor also as carriers forcatalysts.

The'following'examples will serve to illustrate several embodiments ofthe invention and the reenforcing activity of the productsobtained inrubber.

was treated with calcium hydroxide according to the process of theinvention. feldspar were ground with 542 g. of slaked lime(corresponding to 381 g. CaO) and 2 liters of water in a ball mill for24 hours. Thereafter, the ground product was suspended in 8 liters ofwater in an autoclave and treated therein with stirring for 2.5 hours at200 C. After cooling down the reaction mixture the solid reactionproduct was filtered off and dried. The resulting voluminous whitepowder was then tested for its. activity as a reenforcing filler innatural rubber. The quantity employed was parts of the silicate fillerper parts rubber. i

For this purpose 600 g. of the The-vulcanizates produced .had the.following technical properties -A sodium-feldspar of the followingcomposition was treated in the same manner as in Example 1:

Percent SiO 70.32 A1 17 .94 F6203 K 0 1.52 Na O 7.89

The molar ratio of SiO; to calcium hydroxide again was maintained at1:1.

The resulting voluminous white powder was also tested as in Example 1 asa filler for rubber and the vulcanizates obtained had the followingtechnical properties:

vulcanization time, minutes. 5 8 10 Tensile strength, kg./cm.=...- 248218 198 188 181 o 300;kg./cm. 111 93 77 59 60 Elongation on break,percent Elasticity, percent.

52 48 49 45 41 Shore hardness... 74 '73 67 75 Impact resistance, 8. 3 9.2 7. 7 10.1 10.4 Abrasion loss, mmk. 252 244 Specific weight; 1. 281

Example :3

A leucite whose 'SiO content was relatively low of the followingcomposition:

Percent SiO 55.20 A150 20.48 Fe Q 5.22 MnO 2.10 CaO .22 K 0 10.23 N3303.50

was given a hydrothermal treatment analogous to that described inExample 1 except that the molar ratio of vSiO in the leucite to thecalcium hydroxide employed was.1:1.2.

The resulting voluminous powder was also tested as in -Exarnple l as afiller for rubber and the vulcanizates .obtained had the followingtechnical properties:

A comparison of the properties attained in Examples j2and3 clearly showsthat .the use of an excess of calcium hydroxide-favorably influences theimpact resistance .of Qthe vulcanizates-obtained. lThis advantageousproperty which'is attained with use of excess of lime ismore clearlydiscernible in the following example. i

4 Example 4 Two batches of petalite of the following composition:

Percent SiO- 75.3 A1 0 14.5 Li O 3.9 F6203 0.3 Other alkaline oxides 0.6

were given a hydrothermal treatment analogous to that described inExample 1, the molar ratio of Si0 to calcium hydroxide being 1:1 in thefirst batch and 1:125 in the second batch.

The resulting voluminous powders were then tested as in Example 1 as 'afiller for rubber and the vulcanizates obtained had the followingproperties:

Mol ratio SiO :Ca(OH) =1:1

Vuleanization time, minutes. 5 8 .10 V 15 20 Tensile strength, kgJcmfi.182 170 159 153 146 Mod., 300 kg./cm.'- 75 61 53 45 42 Elongation onbreak per- Shore hardness 68 a 65 63 61 60 Impact resistance, kgJcm. 9.5 9. 4 10. 1 10.3 10. 2 Abrasion loss, mm. 212 210 Specific weight 1.298

-Mol ratio SiO2: Ca(OH)z=121.25

Specific weight This example indicates that the use of an excess ofcalcium hydroxide according to the preferred modification of theinvention causes a considerable increase in the impact resistance of thevulcanizates produced so that an outstanding active reenforcing fillercan be easily obtained from a cheap raw material. It must also-bepointed out that when lithium or cesium minerals are employed as thestarting materials the process according to the invention renders itpossible to recover these valuable metals in good yieldsin the form oftheir pure compounds inaddition to the production of a valuable filler.

The properties of the new fillers in the rubber mixtures according toExamples 1 to 4 have been ascertained from mixtures .of the followingcomposition:

powdered silicates suited as filling materials which comprises reactinga naturally occurring alkali metalaluminum double silicate mineral withan alkaline earth metal hydroxidein the .form of .an aqueous suspensioncontainingsat least 5 parts by weight of water per partby weight oftotalsolids at .superatmospheric pressure and ,a temperature between 150and 280 C. until.a.powdered silicate product is obtained, the poured andshaken weight 5 of which is about /3 to /s of those of the startingmaterial, the quantity of alkaline earth metal hydroxide present in suchsuspension being at least 0.5 mol per mol of S10 present in said doublesilicate.

2. The process of claim 1 in which said alkaline earth metal hydroxideis calcium hydroxide.

3. The process of claim 1 in which the quantity of alkaline earth metalhydroxide is at least 0.75 mol per mol of Si0 in said double silicate.

4. The process of claim 1 in which the quantity of alkaline earth metalhydroxide is 1.1 to 1.3 mol per mol of SiO in said double silicate.

5. The process of claim 1 in which the quantity of alkaline earth metalhydroxide is 1.15 to 1.25 mol per mol of Si0 in said double silicate.

6. The process of claim 1 in which the ratio of total solids to water byweight is 1 to at least 8.

Behrman Apr. 29, 1930 Kloepfer et al Apr. 17, 1956 OTHER REFERENCESMellor: A Comprehensive Treatise on Inorganic and Theoretical Chemistry,pp. 691 and 698, vol. 6, Longmans, Green and Co., New York, 1925; page573, last 15 paragraph, 574, first paragraph.

Freidel et al.: (1890).

Comptes Rendus, 110 -1170-1178

1. A PROCESS FOR THE PRODUCTION OF LIGHT VOLUMINOUS POWDERED SILICATESSUITED AS FILLING MATERIALS WHICH COMPRISES REACTING A NATURALLYOCCURRING ALKALI METALALUMINUM DOUBLE SILICATE MINERAL WITH AN ALKALINEEARTH METAL HYDROXIDE IN THE FORM OF AN AQUEOUS SUSPENSION CONTAINING ATLEAST 5 PARTS BY WEIGHT OF WATER PER PART BY WEIGHT OF TOTAL SOLIDS ATSUPERATMOSPHERIC PRESSURE AND A TEMPERATURE BETWEEN 150* AND 280*C.UNTIL A POWDERED SILICATE PRODUCT IS OBTAINED, THE POURED AND SHAKENWEIGHT OF WHICH IS ABOUT 1/3 TO 1/5 OF THOSE OF THE STARTING MATERIAL,THE QUANTITY OF ALKALINE EARTH METAL HYDROXIDE PRESENT IN SUCHSUSPENSION BEING AT LEAST 0.5 MOL PER MOL OD S1O2 RESENT IN SAID DOUBLESILICATE.